CHARACTERS OF MAMMALIAN TEETH. 261 



the close coadaptation of tlieir opposed surfaces, and by 

 the firm adhesion of the alveolar periosteum to the orga- 

 nized cement which invests the fang or fangs of the tooth. 



True teeth implanted in sockets are confined, in the 

 mammalian class, to the maxillary, premaxillary, and 

 mandibular, or lower maxillary bones, and form a single 

 row in each. They may project only from the premaxil- 

 lary bones, as in the narwhal, or only from the lower 

 maxillary bone, as in ziphius; or be apparent only in the 

 lower maxillary bone, as in the cachalot ; or be limited to 

 the superior and inferior maxillaries, and not present in 

 the premaxillaries, as in the true j^eccora (cow, sheep), 

 and most hruta (sloth, armadillo) of Linnaeus. In general, 

 teeth are situated in all the bones above mentioned. In 

 man, where the premaxillaries early coalesce with the 

 maxillary bones, where the jaws are very short, and the 

 crowns of the teeth are of equal length, there is no vacant 

 space in the dental series of either jaw, and the teeth de- 

 rive some additional fixity by their close apposition and 

 mutual pressure. Ko inferior mammal now presents tbis 

 character; but its importance,, as associated with the 

 peculiar attributes of the human organization, has been 

 somewhat diminished by the discovery of a like contigu- 

 ous arrangement of the teeth in the jaws of a few extinct 

 quadrupeds, e. g. anoplotherium, nesodon, and dichodon. 



Structure. — The teeth of the mammalia usually con- 

 sist of hard unvascular dentine, defended at the crown by 

 an investment of enamel, and everywhere surrounded by 

 a coat of cement. The coronal cement is of extreme 

 tenuity in man, quadrumana, and the terrestrial carnivora; 

 it is thicker in the herbivora, especially in the complex 

 grinders of the elephant. Vertical folds of enamel and 

 cement penetrate the crown of the tooth in the ruminants, 



